The invention relates to a method for activating an illuminator and an illumination device, and more particularly to a method for activating a cold cathode fluorescent lamp and illumination device utilizing the heat and light transformation effect of the cold cathode fluorescent lamp.
A light source is needed to illuminate a document to be scanned when a scanner is being operated, in order to allow the CCD (Charge Coupled Device) in the scanner to obtain image data of the document. Thus, the scanning ability of a scanner depends on the functionality of the light source.
Considering the recent trend to reduce scanner volume, the light source must also be made smaller. Therefore, the cold cathode fluorescent lamp (CCFL) is mostly used in scanners. The scanner cannot be operated until the cold cathode fluorescent lamp reaches a certain temperature; otherwise the light emitted from the fluorescent lamp is unstable. So, time must be spent to heat the cold cathode fluorescent lamp sufficiently before a scanner starts to operate. Then, the cold cathode fluorescent lamp can finally illuminate stably after warm-up time.
The life span of the cold cathode fluorescent lamp must be also taken into consideration. If the life span of the cold cathode fluorescent lamp is to be extended, the warm-up time must also be extended. This is the primary reason why the warm-up time of the cold cathode fluorescent lamps of most scanners is three minutes or so. However, most customers complain that this warm-up time is too long.
Therefore, U.S. Pat. No. 5,907,742 discloses a method for warming up the cold cathode fluorescent lamp quickly; it uses a method involving dual-voltage control. During the warm-up period, a higher input voltage (12 volts) is used; then the lower input voltage (approximately 8 volts) is used after the warm-up. The method disclosed in this patent can lower the warm-up time of the cold cathode fluorescent lamp to approximately 10-30 seconds. However, the method of this patent involves a quick warm-up through a higher voltage at the start of the warm-up, which also means that the cold cathode fluorescent lamp must bear a higher current during the warm-up period. This reduces the life of the cold cathode fluorescent lamp, which will be clarified in the following description.
Please refer to FIG. 1, which shows the life curve of the cold cathode fluorescent lamp at different currents. At higher currents, its life is much shorter. As an example, if it lights 15,000 hours continuously at currents of 5 mA and 10 mA, the life of the lamp at 10 mA is 10% shorter than the one at 5 mA. This is the first deficiency of the patent. Furthermore, the patent uses a pulse width modulation (PWM) control circuit to control input voltage for attaining two different input voltages (warm-up period and working period), which makes the design of circuit more complex. Finally, the patent uses a built-in frequency oscillator. Its oscillating frequencies float at different voltages and temperatures, and an unstable light emission occurs between 35 and 45 kHz, influencing scanning ability.
Another method of rapid illumination is to install an additional electric heating wire outside of the cold cathode fluorescent lamp. This method involves winding the electric wire around the cold cathode fluorescent lamp, utilizing the heat of the electric heating wire outside of the lamp to quickly increase the temperature of the lamp. Although this method can attain fast warm-up, a few steps in the manufacturing process must be added to the electric heating wire installment outside of the lamp. Besides, the wire installment increases expenses in furnishing and electricity. Among these deficiencies, the most serious is that the electric heating wire outside of the lamp may block light coming from the lamp, making the illumination of the lamp uneven, which also influences scanning ability.
Therefore, the present fast warm-up methods for cold cathode fluorescent lamps have certain limits and deficiencies. So, how to warm-up the lamp quickly, extend the life span of the lamp, and most importantly emit stable light, has become a very important research topic on the scanning application of the cold cathode fluorescent lamp.
The objective of the invention is to provide a method for activating an illuminator and illumination device, enabling the illuminator to illuminate fast and emit stable light.
The invention uses pins on an application specific integrated circuit (ASIC) in a scanner to output pulses of different frequencies. The illuminator has different efficiencies at different frequencies, so the heat generated by the illuminator at the frequencies of inferior efficiency is used to attain the fast warm-up.
The method of the invention uses a fixed voltage as a voltage of the illuminator, and includes the following steps. Firstly, measure the curve of light efficiency response and frequencies of the illuminator to decide the best light emitting frequency, the best warm-up frequencies and required warm-up time. Secondly, provide a dual-frequency control unit to control the output frequencies of the voltage. When operating the illuminator, the voltage at the best warm-up frequency of the illuminator mentioned above is provided; and after warm-up time, the dual-frequency control circuit is used to provide the voltage source of the best light emitting frequency mentioned above.
The best light emitting frequency and the best warm-up frequency can be obtained from the light efficiency curve of measured frequencies. The frequency at the highest light efficiency is the best light emitting frequency, and the frequency at little lower light efficiency can be chosen as the best warm-up frequency. The warm-up time can be obtained by calculating the time needed for the energy output from the voltage source to be transferred to the heat required to warm-up the illuminator according to the light efficiency of the best warm-up frequency. In practice, the best warm-up frequency is 30 kHz and the best light emitting frequency is 60 kHz. However, the best warm-up frequency and the best light emitting frequency are different for illuminators with different lamp lengths and radii. Therefore, the best warm-up frequency and the best light emitting frequency can be found by experimenting with different lamp lengths and radii.
A warm-up frequency control command is delivered to the voltage source after the dual-frequency control unit receives an activating signal, and then the voltage of the best warm-up frequency is sent out from the voltage source. A working frequency control command is delivered to the voltage source from the dual-frequency control unit after the warm-up time is up, and the voltage of the best light emitting frequency is sent out from the voltage source.
The invention further provides a light emitting device, which includes a light emitter utilized to receive an output voltage in order to emit light, a pulse output unit utilized to generate a pulse of the best warm-up frequency and the best light emitting frequency, a transistor oscillator used to drive and control the pulse output unit to output the pulses of the best warm-up frequency and the best light emitting frequency, and a source of electricity connected with the pulse output unit and light emitter that is used to receive the pulses of the best warm-up frequency and the best light emitting frequency from the pulse output unit in order to generate the electricity supply voltage of the best warm-up frequency or the best light emitting frequency to become the output voltage of the light emitter.
The electric power supply unit further comprises a voltage input unit, switch unit and transformer. The on/off switch is controlled by the pulses of the best warm-up frequency and the best light emitting frequency in order to switch on and off the connection between the voltage unit and transformer to form the output of the working voltage.